Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$232.67	9.738%	$255.3274	$255.33	$255.35	$255.30
Purchase #2	$88.74	13.469%	$100.6924	$100.69	$100.70	$100.70
Purchase #3	$101.42	11.163%	$112.7415	$112.74	$112.75	$112.70
Purchase #4	$167.40	13.548%	$190.0794	$190.08	$190.10	$190.10
Purchase #5	$41.71	3.241%	$43.0618	$43.06	$43.05	$43.10
Purchase #6	$177.82	6.537%	$189.4441	$189.44	$189.45	$189.40
Purchase #7	$103.97	12.360%	$116.8207	$116.82	$116.80	$116.80
7 purchase totals =	$913.73		$1,008.1673	$1,008.16	$1,008.20	$1,008.10